<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
    <style>
        div{
            height: 20px;
            width: 20px;
        }
        #test1{
            background-color: red;

        }
        #test2{
            background-color: green;
            float: left;
        }
        #test3{
            height: 30px;
            background-color: yellow;
        }
    </style>
</head>
<body>
<div id="test1"></div>
<div id="test2"></div>
<div id="test3"></div>
</body>
</html>